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All sunscreens are designed to prevent the transfer of energy from solar rays to skin. Results of solar energy striking skin over time are sunburn, uneven pigmentation, photoaging and an increased risk of skin cancer. The consistent application of adequate amounts of sunscreen lessens all these risks. Even one severe sunburn increases the risk of skin cancer, so sun-damage prevention is a very important issue. Ninety percent of nonmelanoma skin cancer and 65% of melanoma skin cancer are related to UV exposure.1 Up to 90% of all skin changes related to aging are caused by sun exposure.2 Although clients with darker skin types (Fitzpatrick V and VI) may have a decreased risk of skin cancer, UV exposure still significantly increases their chances of developing the condition.

Types of sunscreen

Although they chemically behave differently, there are two broad sunscreen classifications, both of which decrease solar damage by either blocking or absorbing solar energy transfer: physical sunscreens and chemical sunscreens.

Physical sunscreens. Physical sunscreens help prevent solar energy from striking the skin. Although very efficient at deflecting the sun’s rays, a small amount still penetrate the sunscreen barrier and strike skin where they can be absorbed. Zinc oxide and titanium dioxide are physical sunscreens. Physical sunscreens are inert, meaning they do not react with skin. Because they do not affect skin negatively and do not cause skin sensitivity themselves, physical agents are usually preferred for sun protection.

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Chemical sunscreens. There are a large number of chemical sunscreens. All work by absorbing solar energy themselves and transforming it into a chemical reaction, thus preventing transfer of this energy to skin. After absorption of the sun’s energy into the chemical sunscreen molecule, one of two things can happen. This molecule can be chemically transformed via a chemical reaction into another chemical, which is then very quickly converted back to the original sunscreen molecule, ready to absorb another packet of solar energy. This first type of reaction is the most common.

An alternative chemical reaction can occur, which produces a toxic byproduct that itself is carcinogenic. Considerable debate has occurred about how great a problem these small amounts of toxin really are, and if they could potentially increase skin cancer risk. Present consensus is that there is an overall decrease in skin cancer risk from using sunscreen, even allowing for the carcinogenicity of the small amounts of byproduct produced.

Another potential problem associated with use of chemical sunscreens is skin sensitivity. As the sun protection factor (SPF) number increases, the risk of skin sensitivity to the chemical sunscreen also increases. Sunscreen sensitivity is particularly common in young children and those with sensitive skin, fair skin and lower Fitzpatrick skin types, such as people of Irish and Nordic descent. Furthermore, application of chemical sunscreens on fair and sensitive skin can cause photosensitivity and, when exposed to the sun, severe skin inflammation or even blistering can result.

See Sunscreen Ingredients and Protection, which lists the range of UV protection provided by various sunscreens.

Sunscreen formulating technology

Opacity of physical sunscreens used to be a significant problem. Zinc oxide and titanium dioxide are pasty white if applied in their usual chemical form. Advances in formulating technology with nanoencapsulation and microencapsulation of these actives solved the problem of cosmetic appearance. Encapsulation places a tiny amount of the sunscreen inside a chemical container or envelope. Nanocapsules are, in general, below 150–200 nm in diameter, although there is no strict cut-off point for size. Microcapsules are slightly larger than nanocapsules, but still contain a small amount of sunscreen within an envelope.

Although some organizations have questioned the safety of titanium and zinc nanoparticles in sunscreens, both the U.S. Cosmetic Ingredient Review board and the American Academy of Dermatology (AAD) have said they are safe and have improved sunscreen effectiveness. Chemical sunscreen actives may also be microencapsulated, thus allowing smaller amounts to be used and lessening the risk of skin irritation from them.

Protection conveyed by sunscreen

Protection conveyed through the range of UV light varies considerably, depending on the sunscreen active. Zinc oxide provides the most extensive protection throughout both the UVA and UVB ranges of solar energy. Combinations of sunscreen actives are often chosen in order to provide a more comprehensive or efficient range of UV protection.

Two types of solar UV rays strike skin: UVA and UVB. UVA rays (320–400 nm wavelength) carry more energy and penetrate deeper than UVB rays (280–320 nm wavelength). UVA rays can penetrate through the deep dermis into subcutaneous tissue, whereas UVB rays penetrate only slightly into the dermis. Due to ozone layer-thinning in the Earth’s atmosphere, more UVB rays now strike the skin. UVA rays are heavily associated with the changes of aging skin. Both UVA and UVB exposure increase skin cancer risk.

UVA protection. Worldwide, there are several different ways of measuring UVA protection. Sunscreens that give both UVA and UVB protection are called “broad spectrum.” In the United States, much discussion occurred about which UVA measuring system to choose. The U.S. Food and Drug Administration (FDA) decided that sunscreens with an SPF of 15 or greater—because they also protected from some UVA damage—could be labeled as broad spectrum.

UVB protection. Protection from UVB rays is measured by the SPF number. When a sunscreen is given a SPF number, the degree of redness occurring when a specific amount of UVB rays strike skin over a period of time is measured. As is seen in SPF vs. UVB Protection, SPF 30 is not twice as protective as SPF 15. SPF 15 gives 93% redness protection while SPF 30 gives 97% redness protection from a specified amount of sun exposure provided during testing.

As the SPF number increases above 30, the amount of protection given begins to fall off quite rapidly. Because of this, the FDA has stated that a SPF above 50 gives no more meaningful protection than SPF 50, and the maximum labeling should be SPF 50+.3 (See FDA Sunscreen Labeling Requirements for more info about the new sunscreen labels.)

Furthermore, sunscreen alone cannot fully protect from the sun. Consequently, shelter should be sought when your shadow is shorter than you are and protective clothing should be worn, such as a wide-brimmed hat and long sleeves.

Sunscreen application

Clients generally use too little sunscreen and fail to reapply often enough. Much more sunscreen is used for SPF testing than people actually apply themselves. Unfortunately, this means that sunscreen protection is usually inadequate. It is best to apply sunscreen 15 minutes before going outside, and it should be reapplied every two hours, and more frequently with water exposure, sweating and sports participation. The amount applied should be adequate to generously cover unclothed areas of the body, which is at least 1–2 ounces if fully clothed. The lips should also be protected.

Sunscreen and vitamin D

Sunlight is required for the conversion of vitamin D in skin to its active form. Low vitamin D levels have been associated not only with osteoporosis and bone fractures, but also with numerous other medical conditions, including depression, schizophrenia and other mental illness; immune problems; tuberculosis; pneumonia; colds and flu; dementia; cancer of many types; psoriasis; diabetes; hypertension; muscle diseases; and multiple sclerosis.4 Many people have low vitamin D levels, not only in higher latitudes, but even in equatorial zones.5 Clients with more melanin in their skin may metabolize vitamin D more slowly into its active form.

So, does sunscreen application lower vitamin D levels? Medical studies have usually failed to support this concern, possibly because people apply too little sunscreen.6

Many studies in a variety of countries have documented the huge savings in health costs if clients would regularly take a vitamin D supplement.7 In the United States alone, giving 1,000 IU of daily vitamin D to each person would potentially save $16–25 billion in cancer costs every year and cost only $1 billion annually to provide.8 Considering this, it is probably best to recommend measuring vitamin D levels, as well as starting vitamin D supplementation under a physician’s direction in sunscreen users, as well as many other clients.

REFERENCES

BK Armstrong and A Kricker, How Much Melanoma is Caused by Sun Exposure? Melanoma Research 3 395–401 (1993)

IARC Handbooks of Cancer Prevention, International Agency for Research on Cancer, IARC Working Group 5 (2001)

Charlene DeHaven, MD, is the clinical director of Innovative Skincare, maker of iS Clinical products, and is board-certified in both internal medicine and emergency medicine. DeHaven supervises the domestic and international clinical and research aspects of the company.